ofz#6891 empty vector access

Change-Id: Ic36d03d2646ebd90bea5fa91bc4dac3596a55d4a
Reviewed-on: https://gerrit.libreoffice.org/51224Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/qa/core/data/html/fail/ofz6891-1.html

+<table align=left><td><table><S STYLE="position:absolute;width: 6">
\ No newline at end of file

sw/source/filter/html/htmltab.cxx

@@ -2404,7 +2404,10 @@ void HTMLTable::MakeTable( SwTableBox *pBox, sal_uInt16 nAbsAvail,
     // Only tables with relative width or without width should be modified
     m_xLayoutInfo->SetMustResize( m_bPrcWidth || !m_nWidth );
 
-    m_xLayoutInfo->SetWidths();
+    if (!pLine1->GetTabBoxes().empty())
+        m_xLayoutInfo->SetWidths();
+    else
+        SAL_WARN("sw.html", "no table box");
 
     const_cast<SwTable *>(m_pSwTable)->SetHTMLTableLayout(m_xLayoutInfo);